An automated guideway system utilising vehicles which each accommodate, for example, between eight and twenty four passengers would typically operate on guideways separated from other vehicular traffic and pedestrians. Due to economic considerations, the installation of automated guideway transit systems in the suburbs or central business districts of cities will necessitate that the guideway track be elevated above street level rather than underground and will generally be carried on a structure comprising concrete or steel beams supported on pillars. Such guideway tracks must be capable of sharp turns at city intersections in order to reduce the cost of building resumptions.
In order to be acceptable in the abovementioned environment, the guideways should be of least width in order to minimise the visual impact and shade, and the system must also operate with low noise and vibration levels. In order for such systems to be easily accessible to users, the elevated guideways should be able to descend and ascend on ramps, so that vehicles can be accessed from street level when necessary. In addition, the vehicles must also have adequate acceleration and braking capability, and be capable of very short emergency stopping distances needed if they are to operate at high speeds and at close intervals.
Typically, in prior art rapid transit systems such as the TNT Harbourlink operating at Darling Harbour, Sydney which operates on the Von Roll system and detailed in Australian Railways, Volume 2, No 1, February/March, 1988, the vehicles are equipped with rubber tire pneumatic main drive wheels with solid rubber tire wheels engaging the side faces of the guideway beam (or track) for directional control. Additional solid wheels are provided clear of the underside of the upper flange of the beam as a safeguard against overturning. The main wheels are generally pneumatic, which due to their compliance, provide poor lateral and rolling support when operating on a narrow guideway and therefore preclude operation at high speed. If rigid wheels are used, made from steel for example, the stability problems of the abovementioned pneumatic tire vehicles can be overcome. Flanges can also be used on such steel wheels to provide lateral constraint to the vehicle on the guideway.
However, some problems exist with utilising vehicles with either rigid or pneumatic tire driven wheels which are detrimental to the operation of known prior art transit systems. One problem is that such vehicles are prone to slippage during braking, acceleration or grade climbing, particularly in wet or icy conditions. This problem is even more serious when considering the operation of vehicles on an automated guideway system as such an operation is insensitive to weather conditions. Another problem associated with driven rigid wheels, and in particular with steel wheels, is that they tend to be noisy, particularly if provided with a flange that comes in contact with the side of the guideways in turns.
Prior art automated rapid transit systems which do not suffer from slippage problems during wet or icy conditions are The M-Bahn System, detailed in the paper entitled The German M-Bahn System by H. Weinberger in The Journal of Advanced Transportation, Vol. 19:1, pages 73-84, 1985 and in the paper entitled The Taxi 2000 Personal Rapid Transit System by J. Edward Anderson, in the Journal of Advanced Transportation, Vol. 22, Spring 1988. However, these systems operate using electromagnetic linear induction motors for propulsion rather than conventional electric motor drive to the wheels. Whilst such systems overcome some of the earlier mentioned slippage problems, during acceleration or grade climbing, they inevitably lack emergency braking capability needed to achieve close spacing of vehicles when travelling at higher speeds. Moreover, they are costly and less efficient than direct drive systems. The leakage of electromagnetic flux from such linear motors is also a problem. Such systems may not be suited to use when the guidance track incorporates sharp horizontal or vertical curves, due to the close clearance required between the active member of the linear motor suspended on the vehicle and the motor plate supported on the guideway.